Process for preparing a carbonaceous material



Jan. 13, 1959 Feed F. L. SHEA, JR 2,868,695

PRocEss FoR PREPARING A cARBoNAcEous MATERIAL Filed April 18, 1955 l United States Patent C) PRUCESS FOR PREPARIN G A CARBONACEOUS MATERIAL Frederick L. Shea, Jr., Arlington Heights, lll., assignor to Great Lakes Carbon Corporation, New York, N. Y., a corporation of Delaware Application A piil 1s, 1955, serial No. 502,122y

9 claims. ((11.202-9) This invention relates to a novel process for the preparation of a carbonaceous product by heat treatment of a solid, bituminous material. More particularly, this invention relates to a process for preparing a carbonaceous product suitable as a filteraid by heat treatment of a bituminous material normally solid at .ordinary temperatures and capable of expanding on heating to plasticity.

The most commonly used lteraid in the filtration of water and industrial liquids for the removal of finely divided colloidal and mucilaginous suspensoids involves the use of specially prepared diato-maceous earth filteraids. These are selected from particular diatom strata and their manufacture usually involves calcination at an elevated temperature with or Without a uxing agent. Diatomaceous filteraids are to be contrasted with such agents as sand, pumice, gravel, etc. which merely effect a rough straining of the liquid leaving colloidal particles suspended in the filtrate and which cannot be classed as true filteraids. IFiltration with diatomaceous earth filteraids is usually carried `out by admixing small proportions of the powderedagent with the liquid and filtering the liquid through Ia medium (screen, cloth or other readily permeable support) on which the filteraid and entrained suspensoids are retained while the clear liquid passes through. Alternatively, or in conjunction with `the practice just described, a precoat of filteraid may be built up on a iiltration apparatus (rotary or plate and frame filter process) and liquid passed through it to remove the suspended matter. i l,

' Up to the present time the filtration of an alkaline liquid with diatomaceous earth, especially at high temperatures, has been diicult and often impossible. This is due to the rapid rate of solution of diatomaceous silica in the alkaline liquid accompanied by an adverse result upon the structure of the filteraid with attendant reduction in liow rate. Where the suspended matter in suchliquids is of large particle size, resort has been had to ground,

washed anthracite fines which are only about as effective as regular sand filters. In the event that the suspended matter is of finer particle size, use has been made of certain chars recovered from the dehydration and oxidation of black liquors, a by-product ofy paper manufacture. 'I'his liquid is evaporated to recover soda ash by spraying it into a kiln internally heated by combustion of solid fuels. A charred product results from which the inorganic soluble chemicals are recovered by leaching with water, leaving an insolublechar which is reasonably low in ash. Since this is classified as a by-product it varies in quality and is also characterized by a fairly high degree lof activation and friability. The latter property is considered to be objectionable 4since the particles degrade or break down readily during handling and also due to the mechanical action of the filtration apparatus. The increased amount of Ifines in the' product sharply reduces filtration ratesV thereby slowing down other depending plant operations.

It is an object of the invention vto provide a process for producing a carbonaceous material capable the surfaces ,ot the particles or it may' consist of contacting 2,868,695 Patented Jan. 13, 1959 lCC of removing finely divided colloidal and mucilaginous suspensoids when employed as a filteraid in the filtration of water and industrial liquids.

It is a further object of the invention to provide a process for preparing a carbonaceous material suitable as a filteraid in the filtration of highly alkaline liquids, particularly where absorption or solution of silica in the clarified liquor would be harmful or objectionable in subsequent operations involving the clarified liquid.

It is a further object of the invention to provide a process for preparing a carbonaceous material of a special type from normally solid bituminous material.

'It is a further object of the invention to provide a process forv preparing a uniform carbonaceous material which is granular, hard, and improved in friability resistance.

The above objects as well as others which will become apparent upon an understanding of the invention as herein described are accomplished by flash-calcining in a gaseous atmosphere containing a limited and controlled amount of oxygen, a finely divided bituminous feed material normally solid at ordinary temperatures and capable of expanding on heating to plasticity; followed by separating the resulting solid particle material from the gaseous products, and finally heating the separated particles to remove volatile matter remaining on the surfaces of the particles.

The term ash-calcination (first stage reaction) as used herein and in the appended claims may be defined as a method whereby finely divided particles of a suitable bituminous material are subjected to a very rapid upheat rate, estimated to be in excess of 2000 F. (particle surface temperature) per second, in a reactor maintained at a temperature of 1150 F. or higher, but sufficient to ignite the particles. This rapid upheat of the particles is conducted in the presence of air or other oxygencontaining gas (or oxidizing gas) the oxygen being present in an amount such that at least 10% of the evolved combustible volatile matter remains unburned. The amount of air or oxygen present 'is sufiicient to make the process self-sustaining while permitting expansion of the individual bituminous particles at a rapid rate but is insuicient to permit more than a minimum burning of the individual expanded first-stage product particles. In general, it has been observed Ithat higher temperatures may be tolerated when larger particle feed sizes are used.

In a broad embodiment of the invention, finely divided bituminous feed material which is normally solid at ordinary temperatures and Which'is capable of expanding onv heating to plasticity, is processed in three stages. -In therst stage, the feed material is fiash-calcined in a gaseous atmosphere containing oxygen in an amount such that at least 10% of the evolved combustible volatile matter remains unburned.

In the second stage of the process the resul-ting ex-y the particles to render them wettable, the term Wettable `being defined in a subsequent part of this description.

the particles with a stream of inert gases, such as flue gas, at a temperature sufficiently high to distill ol the volatile matter remaining on the surfaces of the particles.

The bulk density ofthe final product should be maintained at a value of less than 25 lbs/cu. ft. We have found that the type of product desired can best be produced where the ashcalcining temperature in the iirst stage is maintained at no less than about 1150 F. and no more than about 2000 F., the optimum temperature varying with the feed size and type of bituminous material used. Employment of too low a temperature will result in an insuiiiciently expanded product. Use of too high a temperature will result in undue shrinkage or collapse of the particles and a consequent excessively high bulk density of the product.

Control of the temperature of heat treatment in the first stage is accomplished by regulating the oxygen intake. lt has been found that the required amount of oxygen in standard cu. ft./lb. of bituminous material is between about 2.0 and 4.0 when unheated air is used as the source of oxygen. Lesser amounts of oxygen can, of course, be used if either the feed or the air or oxygen intake are preheated or if the source of oxygen be relatively pure oxygen or oxygen enriched air, etc. in any event, the oxygen should be present only in such an amount that at least of the evolved combustible volatile matter remains unburned. This unburned volatile matter is largely separated from the expanded particles in the second stage separator from which it is conveyed to some disposal point such as combustion chamber 26 illustrated in the drawing. By thus limiting the burning of evolved combustible Volatile matter in the first stage, reactor temperatures can be maintained suliiciently low (2000 F. or lower), to avoid the aforementioned shrinkage or collapse of the bituminous particles.

The expanded particles obtained from the lirst stage will not be wettable, but in the third stage the proper heat treatment is supplied to achieve wettability. This is an important feature of the invention which further distinguishes it from the prior art. The three stage meth od of this invention results in substantially higher yields and quality than could be achieved in, for example, a single stage process in which both expansion and wettability would be sought in the one stage. The process of this invention makes possible controlled expansion of the particles in the iirst stage and controlled heating in the third stage to obtain the desired wettability.

While it is preferable that the source of heat used in each of the stages be the particle itself, it is conceivable and within the contemplation of this invention that a substantial portion of the heat may be supplied by some outside source or auxiliary fuel. The most rapid upheat rates are, of course, obtained using the particle itself as the source of heat.

The raw material employed in this novel process may be any finely divided bituminous material normally solid at ordinary temperatures and capable of expanding on heating to plasticity. By the latter is meant the ability of the material to soften when heated through the plastic state and swell if the volatile matter of each particle is driven off at a suiiiciently high rate. Examples of such materials include both low volatile and high volatile bituminous coals, raw coal tar pitch coke, and coal tar pitch fortified with any of the various thermal blacks or carbon blacks. In any event the processing history of the raw material selected must not include any heating at a temperature high enough to result in a permanently set carbonaceous structure. Any raw material subjected to such temperature will 'ot expand satisfactorily on heating to plasticity under the conditions disclosed herein.

ln preparing the bituminous material described above for the irst stage flash-calcination operation, the material must be suitably ground or milled to produce finely divided particles. This involves the use of a Raymond hammer mill, Babcock and Wilcox ring roller or other appropriate pulverizing apparatus which will reduce the bituminous material to a particle size of about 95 -100 mesh and preferably about to 95% -200 mesh. It has been found that the latter size of feed is to be preferred in order to produce from coal a nal carbonaceous filteraid which will have a particle size falling Within the range of 5 to 140 microns, very little of the product falling outside of this range. I also contemplate under certain circumstances the milling and classification (by either dry or wet methods) of the bituminous feed.

if the liquid to be filtered with the carbonaceous filteraid, whose process of manufacture is described herein, is sutiiciently neutral or has a pH within the range of 6 to 8, the ash content of the tilteraid product is not of prime importance and it will not be necessary to select a raw material having a particularly low ash content. However, as previously stated, the carbonaceous filteraid is particularly well suited for the filtration of highly alkaline systems, wherein the pH will be greater than 10 and often l2 to 13. In such cases it will often be essential that the ash content of the carbonaceous iilteraid produced be controlled as to composition and amount by selection of the raw material to avoid solution of silica, iron or other deleterious materials. In general, we have found that a bituminous material having an ash content of up to 7%, and depending also on the volatile matter content, produces a satisfactory lilteraid for alkaline systems.

In preparing carbonaceous lilteraids by the process described herein, I have found that particularly beneficial results are to be obtained by maintaining the moisture content of the raw material at a value of less than 5% by weight. Excess moisture in the bituminous material fed to the unit in which the ash-calcination is conducted necessitates vaporization of the Water to a temperature above 1150 F., or whatever reactor temperature used, which sharply reduces the rate of temperature rise of the bituminous particles. Often this must be done by burning additional fuel in the unit since excess moisture in the particlesvreduces the temperature of the operation to a point where the desired results are not obtained.

The carbonaceous flteraid, whose process of manufacture is described herein, may have a very narrow particle size distribution depending upon the requirements of the liquid which is to be filtered. For example, a product may consist of particles whose size is less than l0() mesh and not more than 25% -10 microns; or the product may consist of particles whose size is graduated and falls essentially within the range of 5 to 70 microns. Proper particle size distribution may be obtained by air classication of either or both the feed material and the product of any stage employing means known to those skilled in the art of preparing diatomaceous earth filteraids; the product may also be wet classified. Both of these operations are designed to restrict upper and lower limits with respect to the size of the particles.

A usually essential characteristic of a carbonaceous iilteraid is that it be substantially completely wettable in the liquid which is to be filtered. `This is readily determined by placing a small quantity of the lteraid product in a sample of the liquid and agitating the liquid vigorously. If the product is readily dispersed and suspended in the liquid it is said to be wettable A further requirement of the carbonaceous lteraid product produced by the process of my invention is that it have a bulk density of less than 25 lbs/cu, ft. and preferably within the range of 5 to 2O lbs/cu. ft. Bulk density values are determined by permitting the product to fall freely into a graduated cylinder and measuring the loose-settled volume of a given weight of the product.

In addition to the foregoing definitions, thc following will be useful in describing carbonaceous tilteraids produced by the process of my invention:

vThe volatile content of the coalA and cm'bonaceous iilteraid product, exclusive of water, is determined by` a' procedure whichis a modificationof ASTM Procedure No. D271-48. A small sample of the coal or final filter` aid product isheated to 950 C. for five to ten minutes,"

the difference in weight between the sample and the final product being defined as volatile content.

The cake density of a filteraid is measured; by suspending the filteraid in water and passing the suspension have filtration problems as a check against the properties or clarifying power of thefilteraid.

In a preferred embodiment of my invention, finely dividedbituminous coal having a volatile content of between about 15% and about 20%, is'flash-calcined by entraining in an air stream and feeding it into the top of a vertical reactor. Secondary air is supplied to theA reactor to give a total oxygen content of between 2.2 and about 3.5 standard cu. ft./lb. of coaland to produce a reactor temperature between vabout 1350 and h about 1650 F. The expanded solid product of'this first stage is then separated from the gaseous products in a cyclone collector operated at a temperature not less than that at which substantially all of the vaporous products remain in the vaporous state.` In the third stage, the separated particles are conveyed into the top of a second vertical reactor. kSeco-ndary air is supplied to this reactor to produce a temperature sufficiently high't'o burn off residual volatile matter remaining 'onthe lsurfaces of the particles. 11

The foregoing preferred embodiment is illustrated in the accompanying drawing in which the finely divided bituminous coal is fed into the top of pressurized feed*` hopper 1,2 having an agitator 13 (rotating shaft with 'radial spikes) and screw feeder 14. The coal feedfromk screw feeder 14 is entrained in` an air stream and carried to the top of a rst stage reactor 15 into which it is injected preferably through a water cooled nozzle (not shown). Secondary air is added to reactor 15 at a position near the top of the reactor; Temperatures Within this reactor are preferablybetween 1350 and 1650 F. Blower24 is employed to supply both the primary and secondary air streams throughvalves 27 and 28, re-

spectively. The entrainedproduct particles of reactor 15 c arecarried from the bottom of the reactor to" cyclone 16 along with gaseous and vaporous products, where their separation is effected. The gaseous and vaporous products are removed from the top of lcyclone `16 and passed 0.7 ft./second.

' from ..theptop of cyclone 18 to scrubber 19 having Water sprays 35, 36, and 37. Sludgefrom scrubber 19 is de# posited in sludge pot'20r from which it may be conveniently removed. .The finalrfilteraid product passes from the bottom of cyclone 18 through valve 34 into a drum 211., The residence contentV of the particles, the reactor temperatures and dimensions,v feed rates, and the ratio of oxygen to bituminous particles. In a typical installation, reactors 15 and 17 will both have dimensions of 20 ft. in length and inside diameter of 5 ft. In such a case, a particularly useful residence time in the reactors for medium volatile rcoal particles (75% -200 mesh particle size) isfrom 3 tor 30 seconds, or a particlevelocity of from about 7 to In 4order to yfurther illustrate the invention, but with no lintention of beingvlimited thereby, the following ex-l amples are set forth in which various forms of solid bituminous materials were preliminarily ground to suitable particle size, with controlled moisture content, after which the comminuted material was processed in apparatus of the type illustrated in the drawing. l

The percentfash and bulk density or cake density of the resulting products were determined in accordance with the procedures previously mentioned herein. The flow ratio values of the productsA were determined with a 60 Brix aqueous raw sugar solution' at 80 C. The flow ratio figures indicate the relative performance (rate of ow of liquid through the filter cake) of the carbonaceous ilteraids as compared to a standard grade diatomaceous earth filtered. The procedure for determining iiow ratio is as follows:

Io the raw sugar solution is added 0.3% by weight of carbonaceous filteraid based upon the solids content of the sugar solution. The resulting liquor is passed through a one inch diameter filter for a twenty-one minute period, the pressure` on the system being uniformly raised from 10 upl to 40 p. s. i. at three minute intervals (l0 p, s. i. each) during the vfirst nine minutesl of the test. The values are relative with respect to a high quality, free-liowing 'diatomaceous earth filteraid of rate values for carbonaceous filteraids in comparison lto flow vratio (except for that obtained during the first three into combustion chamber 26 where they are burned prior.V

to escape through a stack. Air supplied byblower and l controlled by valve 32`valong with fuel gas is injected into.

the combustion burner to effect the burning of the gases. Blower 23 is employed prior to normal operation'of the plant to supply fuel lgas to `auxilliary vburners in 15.and 17` which bring the reactors up toI operating temperatures. The `product of the second stage operation (cyclone 16) isA removed through seal valve 30 and carried by an air stream supplied by` blower 24 throughvvalve 31 to the top of reactor 17. Seal valve is necessary since reactor 15 and cyclone 16.are maintained under positive pressure whereas reactor 17 is maintained at a negative pressure by blower 22 operating as an exhauster.

Secondary air is bled into reactor 17 through valve.

33"v insufficient quantity to maintain the reactor vtemperature at about 1300 to about 2300 F. The product of reactor. 17 (third stage operation) -is removed from the bottom lof reactor 17 and carried to collector'y this type of diatomaceous earth filteraid permits a prediction of the performance of the former product on other systems which are normally difficult to filter.

The filtrate obtained in the above determination of minutes `which is discarded) is tested optically for transmissionv clarity which is a measure of the clarifying power of the filteraid. The values` given in the examples following are relative to Dicalite Speedplus arbitrarily given the value of 100.

Example N0. 1

sample of Lillybrook N0. 3 mine bituminous coal Ihaving a volatile content of 17% and ash content of 4.3% was milled to -200 mesh. The rst stage reactor 15 was preheatedto a temperature of 1410 F.

by burning gasy supplied by gas vpump 23 to auxiliary burners in the reactor. A stream of the coal was then 7 fed into reactor 15 at a particle velocity of 1.5 ft./second i 50.1% based on the dry weight of feed to the first stage.

.75'4'1116 product had an ash content of 9.23% ,by` weight, y

embodiment above. The maximum temperature in the first stage (reactor 15) Awas 1562" F. The minimum temperature in the second stage (cyclone 16)was 810 F.' The maximum temperaturein the third stage (reactor 17) was 1960 A,

and processing carried out as described in the preferred The feed rate was lbs/hour.

satisfactory vflterai'd product was obtained in a yield of time of the bituminous particles in they reactors k15 and 17 willdepend upon the size and volatile` 'il a cake density of 15.9, lbs/cu. ft, a flow ratio of 173, and a transmission clarity of 44. i

Example No.. 2

An identical lsample of milled coal and the same processing .apparatus as were used in Example No. 1 were employed with slightly diiferent reactor conditions. The feed rate wasV 161 lbs/hour. The maximum temperature in the first stage was 1605 F., the minimum temperature in the second stage was 815 F., and the maximum temperature in the third stage was 2025 F. A satisfactory flteraid was obtained in a yield of 58.0%, having an ash content of 7.88% by weight, a cake density of 17.1 lbs/cu. ft., a ow ratio of 186, and transmission clarity of 44.

Example No. 3

A sample of Red Jacket bituminous coal having a volatile content of 22% and a feed size of 75% -200 mesh was processed as described in Example 1 using a feed rate of 131 lbs/hour, a rst stage reactor maximum temperature of 1492 F., and a third stage reactor maximum temperature of 2025 F. A 42% yield was obtained having as ash content of 5.80% by weight, a cake density of 12.3 lbs/cu. ft., a ow ratio of 198, and a transmission clarity of 29.

ExampleiNo. 4

A simple of Ditney Hill bituminous coal having a volatile content of 36% and a feed size of 63% -200 mesh was processed as described in Example fusing a feed rate of 155 lbs/hour. The maximum reactor temperatures were 1639 F. in the rst stage and 2217 F. in the third stage. A satisfactory filteraid was obtained in a yield of 30.6% having an ash content of 10.11% by weight, a Acake density of 14.9 lbs/cu. ft., a ow ratio of 191 and a transmission clarity of 38.

Example No. 5

A sample of Lillybrook No. 3 mine coal, milled to 75-79% -200 mesh, was processed as described in Example No. 1 above. The feed rate was 138 libs/hour. The maximum reactor temperature in the first stage was 1693 F. The air to Vcoal ratio was 19.3 cu. ft./lb. of coal. A satisfactory filteraid having a bulk density of 18.5 was obtained in a yield of 70%.

Example N 0. 6

A sample identical to that used in Example No. 5 above was processed in the same manner except that the feed rate was 124 lbs/.hour and the maximum rst stage reactor temperature was 1472 F. The air to coal ratio was 17.8 cu, ft./lb. of coal. A 69% yield was obtained of a good fxlteraid having a bulk density of 13.5.

Example No. 7

A sample identical to that used in Example No. 5 above was similarly processed except that the feed rate was 125 lbs./ hour and the maximum reactor temperature in the first stage was 1454 F. The air to coal ratio was 17.8 cu. lft./lb. coal. An excellent yield of 83% was obtained of an yexcellent iilteraid having a bulk density of 12.5.

Example No. 8

The bulk density of the product was extremely f satisfied the requirements of con'irnercialv production.

For a complete understanding of my invention it is pointed out that the reactor temperatures set forth in the various embodiments of my invention are the apparent'atmospheric temperatures, rather than particle temperatures, and are measured `by means of thermocouples inserted into the interior of the reactors through ceramic sealed wells in the reactorwalls.

-t is also to be understood that bituminous materials other than those described in the foregoing examples may be used to produce carbonaceous tilteraids by my invention, provided that these materials are capable of expanding Von heating to plasticity. Also other conventional types of reactor units may be employed as long as they provide the temperature and atmospheric conditions specied in the broad embodiment set forth above. For example, alternative to the vertical reactor 1'7 described in Figure l, `one may employ a thermal liuidizing unit, an externally fired rotary kiln, or a multiple-hearth furnace of the type known as the Herrscholf furnace in which the coal particles are passed progressively down through the unit while being subjected to a stream of hot gases. it is also to be understood that the carbonaceous lteraids produced by the method described-herein may be classied (or milled and classified) by dry or wet methods in order to regulate the flow rate characteristics, particle size, and particle size distribution in accordance with the requirements of the liquid to be filtered. ln general, a reasonable percentage of -10 micron particles will provide improved clarification lwhere this is necessary; a minimum of l0 micron particles will-greatly improve the ow rate properties of the product where clarity of the lfinal solution is not of prime importance.

yIt is also to Ibe understood that I do not intend to limit the uses of the products of my invention to such as filteraids. The carbonaceous material produced by my novel process may very well meet specifications for other uses such as, for example, use as absorbent carbon material employed in liquid oxygen exposives.

Having thus described the nature of my invention and the uses for the product of my invention, but being limited only by the appended claims with respect to the scope of the invention, I claim:

1. A three-stage process for preparing a carbonaceous material `from finely divided bituminous particles having a particle size of 75 ,-100 mesh and which are normally solid at ordinary temperatures and capable of lbecoming plastic and expanding on heating which comprises, in the first-stage, flash-calcining the particles at a temperature between about 1150 to about 2000 F. in a gas stream containing oxygen in an amount between about 2.0 and about 4.0 standard cu. tft/lb. of bituminous particlesrso that at least 10% of the evolved combustible volatile matter remains unburned, the particles being heated at a rate in excess of 2000 F. (particle surface temperatures) per second; in the second stage, separating the solid expanded first-stage product from vaporous products at a temperature not less than that at which substantially all of said vaporous products remain in the vaporous'state; and in the third stage, heating the solid particles from the second stage t0 remove residual volatile matter remaining on the surfaces of the particles to render them wettable, the final expanded product having a bulk density of less than about 25 lbs/cu. ft.

2. A process according to claim l wherein, in the third stagefthe solid particles from the Second-stage are conveyedin and by a gas stream containing oxygen in sucient amount to burn substantially all of the residual volatile matter remaining on the surfaces of the particles.

3. A three-stage process for preparing a carbonaceous material from nely divided bituminousv coal particles having a particle size of 75% -100 mesh and which are normally solid at ordinary temperatures and capable of becoming lplastic and expanding on heating which comprises, in the first-stage, Hash-calcining the particles at a temperature between about l150 to about 2000 F. in a gas stream containing oxygen in an amount between about 2.0 and about 4.0 standard cu. ft./lb. of bituminous particlesrso that at least of the evolved combustible p volatile matter remains unburned, the particles being heated at a rate in excess of 2000 F. (particle surface temperatures) per second; in the second stage, separating the solid expanded rst-stage product from vaporous products at a temperature notless than that at which substantially all of said vaporous products remain in the vaporous state; and in the third stage, heating the solid particles from the second stage to remove residual volatile matter remaining on the surfaces of the particles to render them Wettable, the nal expanded product having a bulk density of less than about 25 lbs./ cu. ft.y

4. The process of claim 3 in which the third stage com- Y vtemperature is between about 1350 between about 15 to 20% by weight which comprises, in Ithe rst-stage ash-calcining the particles at a temperature between about 1150" to about 2000 F. in a gas stream containing oxygen in an amount between about 2.0 and about 4.0 standard cu. ft./1b. of bituminous particles so that at least 10% of the evolved combustible volatile matter remains unburned, the particles being heated at a rate in excess of 2000 F. (particle surface temperatures) per second; in the second stage, separating the solid expanded first-stage product from vaporous products at a temperature not less than that at which substantially all of said vaporous products remain in the vaporous state; and in the third stage, heating the solid particles from the second stage to remove residual volatile matter remaining on the surfaces of the particles to render them wettable, the nal expanded product having a bulk density of less than about 25 lbs/cu. ft.

7. The process of claim 6 in which the amount of oxygen in the first stage is between about 2.2 and about 3.5 standard cubic feet per pound of coal.

8. The process of claim 6 in which Athe flash-calcining F. and about 1650 F. v

9. A process according to claim 6 wherein, in the third stage, the solid particles from the second stage are conveyed in and by a gas stream containing oxygen in suicient amount to burn substantially all of the residual volatile matter remaining on the surfaces of the particles.

References Cited in the le of this patent UNITED STATES PATENTS Goss Sept. 10, 1946 

1. A THREE-STATE PROCESS FOR PREPARING A CARBONACEOUS MATERIAL FROM FINELY DIVIDED BITUMINOUS PARTICLES HAVING A PARTICLE SIZE OF 75% -100 MESH AND WHICH ARE NORMALLY SOLID AT ORDINARY TEMPERATURES AND CAPABLE OF BECOMING PLASTIC AND EXPANDING ON HEATING WHICH COMPRISES, IN THE FIRST-STAGE, FLASH-CALCINING THE PARTICLES AT A TEMPERATURE BETWEEN ABOUT 1150* TO ABOUT 2000* F. IN A GAS STREAM CONTAINING OXYGEN IN AN AMOUNT BETWEEN ABOUT 2.0 AND ABOUT 4.0 STANDARD CU. FT/LB. OF BITUMINOUS PARTICLES SO THAT AT LEAST 10% OF THE EVOLVED COMBUSTIBLE VOLATILE MATTER REMAINS UNBURNED, THE PARTICLES BEING HEATED AT A RATE IN EXCESS OF 2000* F. (PARTICLE SURFACE TEMPERATURES) PER SECOND; IN THE SECOND STAGE, SEPARATING THE SOLID EXPANDED FIRST-STAGE PRODUCT FROM VAPOROUS PRODUCTS AT A TEMPERATURE NOT LESS THAN THAT AT WHICH SUBSTANTIALLY ALL OF SAID VAPOROUS PRODUCTS REMAIN IN THE VAPOROUS STATE; AND IN THE THIRD STAGE, HEATING THE SOLID PARTICLES FROM THE SECOND STAGE TO REMOVE RESIDUAL VOLATILE MATTER REMAINING ON THE SURFACES OF THE PARTICLES TO RENDER THEM WETTABLE, THE FINAL EXPANDED PRODUCT HAVING A BULK DENSITY OF LESS THAN ABOUT 25 LBS./CU. FT. 